Shade Matters. Peter Hoberg Solmetric Corporation

Transcription

1 Shade Matters Peter Hoberg Solmetric Corporation

2 Shade Matters Shade s impact on PV production Cell, module, string, array Example measurements Characterizing shade Why measure shade? Shade measurement strategies Dealing with shade Predicting energy production Ballpark estimates Analytical tools Resources, Questions and Answers

3 Basic PV System Source:

4 Shading: a little bit goes a long way 100% 73% Business Card covering half of one cell

5 Disproportional Impact of Mismatches Source: EFFECTS OF SHADOW ON A GRID CONNECTED PV SYSTEM - N. Chaintreuil, F. Barruel, X. Le Pivert, H. Buttin, J. Merten INES R.D.I., Laboratory for Solar Systems (L2S) Shade Power loss Series connection 0.15% 3.7% 23x 2.6% 16.7% 6x 11.1% 36.5% 3.2x Nine (multi-crystalline) Photowatt PW1650 (4 bypass diodes) connected in series to a SMA Sunny Boy SB1100 inverter Slide courtesy of:

6 Solar Cell Charge generation Charge separation Charge collection Photon + n p

7 I-V Curves I I + + Diode: V Solar cell: V I Forward conduction Reverse breakdown I Power dissipation Power production V V Reverse breakdown

8 Maximum Power Point I Imp Max power Imp x Vmp Contours of constant power generation I x V Vmp v V

9 Cells in Series & Parallel I Max power point I-V curve of the array V

10 Bypass Diodes I BP Cell without bypass diode A Cell with bypass diode B Max Power Wasted power Partially shaded cell Unshaded cell -12 v -0.7 v v V

11 How Cells Become Reverse Biased Vreverse Inverter Inverter N x Vpmax N x Vpmax Vpmax N = # of cells Vnew Vreverse = (N-1) x Vnew N x Vpmax = N x (Vnew Vpmax) - Vnew

12 Typical PV Module Layout Shade Shade +

13 Inverter dynamics

14 Max Power Point Tracking (MPPT) Methods Perturb & observe or hill climbing P/ V Fraction of V oc or I sc Fuzzy logic Neural network Ripple correlation Current sweep Load current or load voltage maximization dp/di or dp/dv feedback control From Comparison of PV array maximum power point tracking techniques, Esram & Chapman, 2007

15 Max Power Point Tracking (MPPT) Perturb & Observe method P P max P max V V + V V

16 The Challenge of Partial Shading P P max Contours of constant power generation ( I x V ) V V + V V

17 Strings in Parallel I String max power points Note: Shaded strings can be further penalized by operating below MPP String I-V curves Vpmax V

18 Shading Demonstration Shading conditions: 1. No shade 2. Shade ½ of one module 3. Shade 1 cell 4. Place credit card on one cell West string East string 2 strings of 12 BP SX120 modules

19 Shading Demonstration

20 PV Array Performance Analyzer

21 I-V Curve of Un-shaded String 1 string of 12 BP SX120 modules (864 cells in series)

22 ½ of One Module Shaded 1 string of 12 BP SX120 modules (864 cells in series)

23 One Cell Shaded 1 string of 12 BP SX120 modules (864 cells in series)

24 Credit Card Placed on One Cell 1 string of 12 BP SX120 modules (864 cells in series)

25 Shade Matters Shade s impact on PV production Cell, module, string, array Example measurements Characterizing shade Why measure shade? Shade measurement strategies Dealing with shade Predicting energy production Ballpark estimates Analytical tools Resources, Questions and Answers

26 Insolation for fixed plane (San Diego)

27 Insolation for fixed plane (Honolulu)

28 Why measure shade? Choose optimum location for panels Identify issues early in the process Ensure sufficient energy production Ensure optimum state rebate Remember: Shading can have disproportionate impact on energy production

29 Shade through a fisheye lens

30 Steps for measuring solar access Bubble Level Compass 1. Point south 2. Hold Level 3. Press the button

31 Shade measurement strategies Take multiple point readings Spacing between readings Look for worst case Array corners Points closest to obstructions Average solar access readings Obstruction elevation angles Note: Be sure you meet the requirements of your state program and rebate calculators

32 Dealing with Shade Optimize Shade-Free production Avoid shade whenever possible Find the best location for the desired season/time-of-day Tree removal Reduce shade Minimize debris Module Level MPP Incorporate new technologies that mitigate shade impact

33 The SolarMagic Power Optimizer SolarMagic Input High speed MPPT algorithms maximize panel energy harvest Wide-input range accommodates almost all panel types SolarMagic Output Automatically scales output current and voltage to optimize power of the entire string. Wide output range maximizes flexibility Slide courtesy of:

34 Shade Matters Shade s impact on PV production Cell, module, string, array Example measurements Characterizing shade Why measure shade? Shade measurement strategies Dealing with shade Predicting energy production Ballpark estimates Analytical tools Resources, Questions and Answers

35 PV energy production Sun Az/El, panel tilt/az Insolation, temp., wind speed Module-level shading Module parameters Inverter parameters, MPP behavior AC kwh

36 Predicting energy production Solar Calculators: PVWatts by NREL Vendor web sites State rebate calculators CSI Incentive Calculator (EPBB Calculator) NSHP Calculator Commercial software products PV*SOL, PV-Syst, Laplace, Maui On-grid, CPF Tools, Clean Power Estimator Etc.

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38 Predicting energy production Calculators available: PVWatts by NREL State rebate calculators CSI Incentive Calculator (EPBB Calculator) NSHP Calculator Commercial software products PV*SOL, PV-Syst, Laplace, Maui On-grid, CPF Tools, Clean Power Estimator

39 Solmetric PV Designer

40 Some References Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques (Esram and Chapman) On-site Measurements of photovoltaic systems for detection of failure modules (Oozeki, Yamada, and Kato) MATLAB-Based Modeling to Study the Effects of Partial Shading on PV Array Characteristics (Patel Agarwal) Effects of Shadow on a Grid Connected PV System, Chaintreuil, Barruel, Le Pivert, Buttin, Merten INES R.D.I., Laboratory for Solar Systems (L2S) PV Watts, CSI Incentive Calculator,

41 Questions?